Universality

When the unusual is familiar, we easily overlook that the familiar is unusual. In this case, I’m thinking of the universal features of life, including the genetic code. The universality of the code (for example) means the code is not represented by a tree (or bush). In my book, I argue “Universality not only argues for common descent, but also argues against a non-teleological origin.” I’m not talking about anything that amounts to a proof, only the direction of the inferential winds (clues). The case for the non-teleological origin of the code would be much, much stronger if we had an array of variant and precursor codes that could be independently scored as reflections of a primordial state, all arranged in a nested hierarchy (I point this out in chapter 10). And it was no less than Crick and Orgel themselves who cited the universality of the code as supporting evidence for directed panspermy.

Yet universality is only a clue because we can plausibly account for it from a non-teleological perspective (much as a teleologist might plausibly account for the backward wired retina or junk DNA). If we had no plausible alternative explanation, universality would be a very powerful argument and not simply a clue.

One way to account for universality is an appeal to panspermy. This is plausible, but I also think it seriously stirs the Rabbit. Consider some points. First, panspermy is an appeal to seeding, and seeding can be either teleological or non-teleological (there’s another rabbit hole). Second, panspermy is essentially an appeal to quasi-discontinuity, as it posits a discontinuity between the Earth itself and the origin of life. If the seeding is non-teleological, this means that the original life forms were not shaped and adapted for life on Earth. Therefore, the success of the seeding would either be attributed to luck (the Duck in all his raw glory) or the laws of physics and chemistry (the Rabbit in the Big Bang).

To escape flirting with discontinuity, another explanation is the bottleneck. After all, the history of life comes with a history of bottlenecks. But in this case, we are talking about a bottleneck that sterilizes the entire planet except for the lineage that has the Code, a code that just turned out to be very hard to alter during the subsequent 3.5 billion years of evolution. Yet consider the size of the chasm between the hypothetical self-replicating molecule floating in the primordial pool of potential biomolecules and the level of complexity and sophistication entailed by the universal features of life. Unless the laws of chemistry front-loaded the universal features, that’s a whole lot of evolutionary ground for a blind watchmaker to meander about in. In other words, the chasm is larger between the self-replicator and the last universal common ancestor (LUCA) than it is between LUCA and humans. What’s more, we are talking about “primitive creatures, with more error-prone translation, fewer gene products, and a lesser penalty for imprecision” (from a review by Yarus). A huge chasm and enhanced plasticity is a recipe for an explosion of permutations. In fact, more so than the entire tree of life that exists today. And what of the timing? Why did this bottleneck event occur after the Code became “chilled”, as the subsequent adaptive radiation (and all this involves) shows no solid trace of continuing with the evolution of the Code or adding more amino acids? It’s quite the coincidence to have the most extreme bottleneck in history occurring just after the genetic code finished evolving.

Could a bottleneck event have reached into all parts of the globe to erase all these variants except for the very one we are trying to account for, one that just happened to be finished with evolving the Code? Sure. But is this indeed THE explanation? And why is it not an ad hoc explanation? At this point, the Rabbit has his demands. Where is the independent evidence for the narrowest of all proposed bottlenecks? What’s more, why did the lineage with the Code survive and not the others? Was there something special about life’s code that allowed it to escape extinction? Or was it just luck? If it is the latter, then that is just the Duck quacking. And the Rabbit fully expects ducks to quack.

Consider some other angles on this issue. Does a non-teleological origin of life predict universal biotic features? Does anyone look at the universal code proclaim, “This is evidence FOR the non-teleological origin of the code”? Or what about falsification? There are millions of uncharacterized microbial life forms out there. The Rabbit predicts they will share the Code. If we find one life form with a significantly different code than can be plausibly scored as “primitive,” the Rabbit is badly hurt. If we find a couple more, the Rabbit must hop back into the Big Bang. What could we find that would weaken the undirected panspermy explanation? What could we find that would weaken the bottleneck explanation? In these regards, can the Duck really match the methodological rigor of the Rabbit?

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One response to “Universality

  1. Pingback: An Exceedingly Exceptional Code «

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